7,983 research outputs found
A strong correlation in radio pulsars with implications for torque variations
We present an analysis of the spin-down parameters for 131 radio pulsars for
which has been well determined. These pulsars have characteristic
ages ranging from yr and spin periods in the range 0.4--30 s;
nearly equal numbers of pulsars have as . We find a
strong correlation of with , {\em independent of the sign
of} . We suggest that this trend can be accounted for by small,
stochastic deviations in the spin-down torque that are directly proportional
(in magnitude) to the spin-down torque.Comment: MNRAS, 4 pages, 2 figures. Minor editorial changes and typos
correcte
SMMR simulator radiative transfer calibration model. 1: Derivation
There are no author-identified significant results in this report
Starquake-Induced Glitches in Pulsars
The neutron star crust is rigid material floating on a neutron-proton liquid core. As the star's spin rate slows, the changing stellar shape stresses the crust and causes fractures. These starquakes may trigger pulsar glitches as well as the jumps in spin-down rate that are observed to persist after some glitches. Earlier studies found that starquakes in spinning-down neutron stars push matter toward the magnetic poles, causing temporary misalignment of the star's spin and angular momentum. After the star relaxes to a new equilibrium orientation, the magnetic poles are closer to the equator, and the magnetic braking torque is increased. The magnitude and sign of the predicted torque changes are in agreement with the observed persistent spin-down offsets. Here we examine the relaxation processes by which the new equilibrium orientation is reached. We find that the neutron superfluid in the inner crust slows as the star's spin realigns with the angular momentum, causing the crust to spin more rapidly. For plausible parameters the time scale and the magnitude of the crust's spin up agree with the giant glitches in the Vela and other pulsars
Sensitivity of an image plate system in the XUV (60 eV < E < 900 eV)
Phosphor imaging plates (IPs) have been calibrated and proven useful for
quantitative x-ray imaging in the 1 to over 1000 keV energy range. In this
paper we report on calibration measurements made at XUV energies in the 60 to
900 eV energy range using beamline 6.3.2 at the Advanced Light Source at
Lawrence Berkeley National Laboratory. We measured a sensitivity of ~25 plus or
minus 15 counts/pJ over the stated energy range which is compatible with the
sensitivity of Si photodiodes that are used for time-resolved measurements. Our
measurements at 900 eV are consistent with the measurements made by Meadowcroft
et al. at ~1 keV.Comment: 7 pages, 2 figure
Correlation of Patient Symptoms With Labral and Articular Cartilage Damage in Femoroacetabular Impingement.
BackgroundFemoroacetabular impingement (FAI) can lead to labral and articular cartilage injuries as well as early osteoarthritis of the hip. Currently, the association of patient symptoms with the progression of labral and articular cartilage injuries due to FAI is poorly understood.PurposeTo evaluate the correlation between patient-reported outcome (PRO) scores and cartilage compositional changes seen on quantitative magnetic resonance imaging (MRI) as well as cartilage and labral damage seen during arthroscopic surgery in patients with FAI.Study designCohort study; Level of evidence, 3.MethodsPatients were prospectively enrolled before hip arthroscopic surgery for symptomatic FAI. Patients were included if they had cam-type FAI without radiographic arthritis. All patients completed PRO scores, including the Hip disability and Osteoarthritis Outcome Score (HOOS) and a visual analog scale for pain. MRI with mapping sequences (T1ρ and T2) on both the acetabular and femoral regions was performed before surgery to quantitatively assess the cartilage composition. During arthroscopic surgery, cartilage and labral injury grades were recorded using the Beck classification. Pearson and Spearman correlation coefficients were then obtained to evaluate the association between chondrolabral changes and PRO scores.ResultsA total of 46 patients (46 hips) were included for analysis (mean age, 35.5 years; mean body mass index [BMI], 23.9 kg/m2; 59% male). Increasing BMI was correlated with a more severe acetabular cartilage grade (ρ = 0.37; 95% CI, 0.08-0.65). A greater alpha angle was correlated with an increased labral tear grade (ρ = 0.59; 95% CI, 0.37-0.82) and acetabular cartilage injuries (ρ = 0.61; 95% CI, 0.42-0.80). With respect to PRO scores, increasing femoral cartilage damage in the anterosuperior femoral head region, as measured on quantitative MRI using T1ρ and T2 mapping, correlated with lower (worse) scores on the HOOS Activities of Daily Living (r = 0.35; 95% CI, 0.06-0.64), Symptoms (r = 0.32; 95% CI, 0.06-0.57), and Pain (r = 0.31; 95% CI, 0.06-0.55) subscales. There was no correlation between PRO scores and acetabular cartilage damage or labral tearing found on quantitative MRI or during arthroscopic surgery.ConclusionFemoral cartilage damage, as measured on T1ρ and T2 mapping, appears to have a greater correlation with clinical symptoms than acetabular cartilage damage or labral tears in patients with symptomatic FAI
Fanthalamia kadiri nov. sp., a new “Sphinctozoan” sponge from the Triassic (Carnian) of Turkey
A new sphinctozoid sponge - Fanthalamia kadiri - is described from the Upper Triassic (Carnian) of the Antalya area, southern Turkey. This is the second species of the genus Fanthalamia found in Upper Triassic rocks of Turkey.Baba Senowbari-Daryan, Michael Link & Diego C. García-Bellid
Tkachenko waves, glitches and precession in neutron star
Here I discuss possible relations between free precession of neutron stars,
Tkachenko waves inside them and glitches. I note that the proposed precession
period of the isolated neutron star RX J0720.4-3125 (Haberl et al. 2006) is
consistent with the period of Tkachenko waves for the spin period 8.4s. Based
on a possible observation of a glitch in RX J0720.4-3125 (van Kerkwijk et al.
2007), I propose a simple model, in which long period precession is powered by
Tkachenko waves generated by a glitch. The period of free precession,
determined by a NS oblateness, should be equal to the standing Tkachenko wave
period for effective energy transfer from the standing wave to the precession
motion. A similar scenario can be applicable also in the case of the PSR
B1828-11.Comment: 6 pages, no figures, accepted to Ap&S
Pulsar Constraints on Neutron Star Structure and Equation of State
With the aim of constraining the structural properties of neutron stars and
the equation of state of dense matter, we study sudden spin-ups, glitches,
occurring in the Vela pulsar and in six other pulsars. We present evidence that
glitches represent a self-regulating instability for which the star prepares
over a waiting time. The angular momentum requirements of glitches in Vela
indicate that at least 1.4% of the star's moment of inertia drives these
events. If glitches originate in the liquid of the inner crust, Vela's
`radiation radius' must exceed ~12 km for a mass of 1.4 solar masses.
Observational tests of whether other neutron stars obey this constraint will be
possible in the near future.Comment: 5 pages, including figures. To appear in Physical Review Letter
Colospongia cribrifera nov. sp. and Parastylothalamia minima nov. sp. ("Sphinctozoa" Porifera) from the Norian of Taurus Mountains, Turkey
uploaded for Revue de Paléobiologie by Plaz
Correlated decay of triplet excitations in the Shastry-Sutherland compound SrCu(BO)
The temperature dependence of the gapped triplet excitations (triplons) in
the 2D Shastry-Sutherland quantum magnet SrCu(BO) is studied by
means of inelastic neutron scattering. The excitation amplitude rapidly
decreases as a function of temperature while the integrated spectral weight can
be explained by an isolated dimer model up to 10~K. Analyzing this anomalous
spectral line-shape in terms of damped harmonic oscillators shows that the
observed damping is due to a two-component process: one component remains sharp
and resolution limited while the second broadens. We explain the underlying
mechanism through a simple yet quantitatively accurate model of correlated
decay of triplons: an excited triplon is long-lived if no thermally populated
triplons are near-by but decays quickly if there are. The phenomenon is a
direct consequence of frustration induced triplon localization in the
Shastry--Sutherland lattice.Comment: 5 pages, 4 figure
- …